The Internet has become a valuable network communication system. It allows people to send communications around the world in a matter of minutes, access websites, and download information from a nearly unlimited number of remote locations. The Internet includes a collection of hosting servers and clients that are connected in a networked manner. In addition to the servers and client computers, there are other significant components that enable the Internet to function. Some of the components the Internet uses to transfer information include routers, gateways, switches, hubs and similar network devices.
One device of interest is a router. Routers can be considered specialized electronic devices that help send messages, information, and Internet packets to their destinations along thousands of pathways. Much of the work to get a message from one computer to another computer on a separate network is done by routers, because routers enable packets to flow between interconnected networks rather than just within localized networks. Routers receive packets from the one or more networks that they are connected to and then determine to which network the packets should be forwarded. For example, a router for a local network may receive a packet that should be kept within the network because it uses a local address. This same router will also receive packets that may need to be sent to the Internet because the packets have an Internet address.
Internet data for a message or file is broken up into packets about 1,500 bytes long. Each of these packets has a wrapper that includes information about the sender's address, the receiver's address, the packet's place in the entire message, and how the receiving computer can be sure that the packet arrived intact. Each data packet is sent to its destination via the best available route or a route that might be taken by all the other packets in the message or by none of the other packets in the message. The advantage of this scheme is that networks can balance the load across various pieces of equipment on a millisecond-by-millisecond basis. If there is a problem with one piece of equipment in the network while a message is being transferred, packets can be routed around the problem, ensuring the delivery of the entire message.
In addition to the addressing information, a packet includes a data portion that is the original information being transmitted. Data packets can be classified by the protocol used to send the information, the application being used to originate the information and the user or machine generating the network traffic, among many others. A data stream that is sent during a session is a plurality of data packets which convey the original message.
Every piece of equipment that connects to a network has a physical address, regardless of whether the equipment is located on an office network or the Internet. This is an address that is unique to the piece of equipment that is actually attached to the network cable. For example, if a desktop computer has a network interface card (NIC) in it, the NIC has a physical address permanently stored in a special memory location. This physical address, which is also called the MAC address (Media Access Control), has two parts that are each 3 bytes long. The first 3 bytes identify the company that made the NIC. The second 3 bytes are the serial number of the NIC itself.
A computer can have several logical addresses at the same time. This enables the use of several addressing schemes, or protocols, from several different types of networks simultaneously. For example, one address may be part of the TCP/IP network protocol or another networking protocol. The network software that helps a computer communicate with a network takes care of matching the MAC address to a logical address. The logical address is what the network uses to pass information along to a computer.